1. Field of the Invention
This invention relates to aluminum alloy compositions consisting essentially of, on the basis of total weight of the composition, 13 to 28 wt % of silicon, 1.5 to 5 wt % of a metal element selected from iron and manganese, 3 to 10 wt % of zinc, 0.5 to 1 wt % of magnesium, and aluminum as balance.
This invention also relates to aluminum alloy products made from said aluminum alloy compositions, the aluminum alloy products exhibiting improved mechanical properties at high temperatures, including excellent wear resistance, hardness and thermal stability.
2. Description of the Related Art
Aluminum alloys have been widely used in the automobile, transportation and other industries due to their high strength-to-weight ratio, superior processing properties and excellent weather-resistance. In early years, aluminum alloys were employed in the industry primarily due to the lightweight characteristics thereof, and the wear resistance of the same was seldom considered. However, since the 1970s, there arose many problems that need to be solved. In the first aspect, due to energy crisis, it was highly desired in industry to manufacture lightweight transportation vehicles that work with high efficiency. In the second aspect, since excellent wear-resistance was an indispensable property for some key components of transportation vehicles, manufacturers in the industry therefore endeavored to develop aluminum alloys with high wear-resistance.
Heretofore, precipitation hardening treatment is the main process used in the art to strengthen the hardness of commercially available aluminum alloys with median or high strength, such as aluminum alloys 2024, 6063, 7075, JIS AC9A, AA A390, etc. Precipitation hardening treatment is primarily conducted as follows: A selected aluminum alloy is heated to a specific temperature lower than the melting point thereof for a period of time, causing the added elements contained in the aluminum alloy to solubilize within the α-Al phase of the aluminum alloy. The above-described operating procedure is called “solid solution treatment.” Once the added elements are completely solubilized within the α-Al phase of the aluminum alloy, the aluminum alloy is immediately immersed into a low temperature medium, so that a super-saturation of the solubilized elements within the aluminum alloy is achieved instead of the formation of precipitated particles from the solubilized elements. The thus-obtained aluminum alloy containing therein a super-saturation of solubilized elements is then placed at a specific temperature to cause particle precipitation from the super-saturated elements within the aluminum alloy. The above-described operating procedure is called “aging treatment.”
The commercially available wear-resistant aluminum alloys, such as JIS AC9A, AA A390, etc., must be subjected to the precipitation hardening treatment in order to obtain a sufficient mechanical strength. However, the precipitation hardening treatment is time-consuming and costly. In addition, if these aluminum alloys are combined with other series of aluminum alloys by “casting in”, their heat treatment conditions will be strictly limited and they may even become unsuitable for heat treatment. With respect to aluminum alloys 2024, 6063 and 7075, if they are held at a temperature higher than 150° C., the precipitates contained in strengthening phase thereof, such as MgZn2 and Al2Cu, will immediately become coarsened, thus deteriorating the strengthening effect of such aluminum alloys. Therefore, aluminum alloys 2024, 6063 and 7075 are only available for use at a temperature below 150° C.
However, with the advancement in the transportation industry, and in view of the increasing need of developing lightweight vehicles, applications of aluminum alloys have been extended to include environments with high temperatures. For example, they may be used to form engine blocks, engine cylinder liners, compressor pistons, disc brakes, etc. Therefore, it has become a very important subject in the light-metal industry to develop aluminum alloys with excellent mechanical properties at high temperatures.
In view of the aforesaid, it is highly desired to develop aluminum alloys that can be formed without precipitation hardening treatment and that exhibit improved mechanical properties at high temperatures, including excellent wear resistance, hardness and thermal stability.